The present invention relates to a circuit pattern inspection technique and, more particularly, to a method and apparatus for observing a fine pattern by using a scanning microscope and inspecting an edge shape of the fine pattern.
In an LSI process, particularly, a microfabrication process performed after ArF lithography in recent years, as a pattern is becoming finer, the problem of roughness at the edge of a pattern is becoming bigger.
The occurrence of roughness is caused by the property of the material itself, exposure equipment, a substrate, or an observing apparatus itself. In a mass production process, the degree of roughness exerts a large influence on the performance of a product. Even when roughness is not abnormally large, appearance of characteristic roughness is often a reflection of deterioration in performance of a manufacturing apparatus, so that a failure may occur in a product in future. Consequently, development of a system for observing the shape of roughness at edges of a pattern and specifying the cause from the characteristic of the roughness is urgently necessary. Considering that the system is used in a mass production process, the inspection method has to be a non-destructive one.
Conventionally, information is empirically obtained mainly by view observation of an observed image by a scanning electron microscope. For example, there is a case that a state where right and left edges fluctuate synchronously can be seen at the time of observing a line pattern of a resist. In this case, the causes can be considered as follows for example: due to a narrow line, the top of a pattern fluctuates at the time of development, a light intensity distribution at the time of exposure fluctuates, and the observed image itself is distorted. There is also a case that roughness is seen relatively small around the surface but is seen large on the bottom portion of a pattern. From such a phenomenon, the possibility that the chemical property of the resist material does not match that of the substrate well and a residual is caused is considered.
However, such criteria of determination are not quantitative, the conclusion varies depending on observers. In order to systematically analyze the cause of occurrence of roughness without depending on the observer, the shape of roughness has to be quantitatively determined.
An example of the conventional attempt to quantitatively express the characteristic of the shape of the pattern edge is disclosed in the document, “B. Su, T. Pan, P. Li, J. Chinn, X. Shi, and M. Dusa, Proc. 1998 IEEE/SEMI Advanced Semiconductor Manufacturing Conference, p259 (1998)”. According to the method, the taper shape of a line pattern edge is expressed by numbers from an SEM image. Although information of the edge portion in a cross sectional shape can be obtained to a certain degree, the characteristic of an edge in the direction along a line edge cannot obtained. A value obtained is an index of inclination of a side face of an edge, so that roughness cannot be evaluated.
A general method of detecting roughness of a pattern edge is a method of obtaining some deviations of edge positions from a straight line and calculating a standard deviation σ in a distribution of the deviations or a value which is three times as large as π. However, the roughness herein denotes accurately a dimensional error as used in the documents, “S. Mori, T. Morisawa, N. Matsuzawa, Y. Kamimoto, M. Endo, T. Matsuo, K. Kuhara, and M. Sasago, J. Vac. Sci. Technol. B16, p739 (1998)” and “C. H. Diaz, H. Tao, Y. Ku, A. Yen, and K. Young, IEEE Electron Device Letters 22, p287 (2001)” and is not an index used to evaluate the shape of an edge.
As described above, conventionally, there is no method of quantitatively evaluating the shape of an edge. Although the stereoscopic shape of an edge can be determined by view observation, it depends on the observer.